The mechanism of phototransduction in a visual receptor remains unsolved. The problem involves the nature of the processes involved between changes of photopigment triggered by light and the ensuing permeability changes of the photoreceptor membrane. The photoreceptors in the lateral eye of the barnacle Balanus eburneus offers an approach to this problem because of their large size (80-100 microns), variegated electrical behavior, and the relative ease of applying different microtechniques. The Balanus receptor potential will be studied in conjunction with a number of different microtechniques: (1) microelectrode recording and membrane polarization techniques (2) Ca2 ion and H ion microelectrodes (3) pressure and iontophoretic injection and (4) single cell spectrophotometry. The primary objective of the investigation is to determine the role of intracellular changes of H ion and Ca2 ion in the production of the receptor potential and adaptation to light. Specific objectives include: (a) Measuring H ion and Ca2 ion activity in Balanus with ion sensitive microelectrodes and absorbance changes. (b) Examine change upon illumination in normal cells and in cells in which electron transport has been inhibited. (c) To relate changes in intracellular Ca2 ion and H ion in Balanus to determine the extent of coupling. (d)To modify internal pH and Ca2 ion activity, quantitate the change and determine the effect on different phases.